It’s interesting that they state that the cannot be sure that the printers that did not create the tracking dots are not using another way to add a tracking code to the printed documents. The printer manufacturers apparently gave in to the demands of the US Government in a “purported effort to identify counterfeiters”.

Currently there is not enough information to validate a tracking dot with a 100% certainty unless the manufacturer himself stated that the printer would indeed make use of it. The EFF has been using three sources of information to compile the list:

We looked at printer output under a blue light and/or a computer microscope; we consulted press reports about printers (e.g. at Druckerchannel); we relied on printer manuals and other manufacturer statements.

The two companies that have a completely green – meaning no yellow dots to be seen – listing are Okidata and Samsung. As the EFF states this does not necessarily mean that they do not use another method to add the information to the printouts but as of know nothing of this kind could be spotted.